Micro-machined hot-wire flow sensor for spirometer

ABSTRACT

A spirometric system can be used to determine static and dynamic lung function for diagnosis, therapy and evaluation. In recent years, air pollution and deteriorating environment cause respiratory diseases increasing rapidly. A portable spirometric system, which for home care and possible screening test in the hospital is the answer to this needs. Recently, the established technologies of microelectromechanical system (MEMS) have enabled the possible minimization of spirometer with microsensor. It includes the modular design for low power consumptions, precision volume productions, competitive price for disposable sensors. In this invention, the focus is to improve sensor&#39;s performance by using MEMS technologies and material selection. Fabricating microsensor uses semiconductor processes, which aims to increases sensor&#39;s performance and lower cost by future mass production. The use of American Thoracic Society (ATS) guidelines for system implementation assures the quality of system for future upscale production of safe and quality device.

BACKGROUND

[0001] In recent years, respiratory related illness like chronic cough, chronic bronchitis, gasp etc. is increasing due to the air pollution and environmental deterioration. The clinical use of some of the medicine may change or improve the respiratory functions of the patients. Generally speaking, the parameters are taken based on the normal and basic volume of the testees using respiratory measurement instrument to determine the static and dynamic lung data. The information is provided for the diagnosis, treatment and tracing, such as the early detection of the lung disease, determination of seriousness, assessment of effectiveness, field or environmental influences, application of medicine and risks of surgery. The present respiratory diagnosis instruments will mainly take measurement of the respiratory volume or flow.

[0002] Volume measurement is to collect the out going air into a container and then measure the continuous change of volume. Respiratory measurement is to take the flow by a converter for the volume calculation. In the Johnson, A T, Bronzino, J D, Respiratory system, The Biomedical Engineering Handbook Ch. 7, pp70-86,; Bronzino J D. mentioned that the parameters taken in different conditions and periods will be treated by the sensor and processor for the diagnosis and judgement of the respiratory function. Those direct data like tidal volume, TV at rest or sports and vital capacity by full play breadth can be thus obtained.

[0003] Other parameters like IRV, ERV, IC can be made out by calculation. FVC is taken by the similar principle, so are the following FEV, PEF, MMEF and MVV.

[0004] While the method of measurement is by volume and flow calculation, the respiratory measurement will be directional as the design and usage being similar and the portable or desk top models will prevail. in terms of convenience and miniature. The flow models available nowadays are generally in 4 types:

[0005] 1. Differential air pressure/velocity; 2. Thermal resistance; 3. Turbine meter; 4. Ultrasonic flow meter.

[0006] American patent U.S. Pat. No.5460039 indicates that the system of measurement of air velocity will include the traverse and parallel thermal resistance to the direction of the air flow but with less convenience and portability. American patent U.S. Pat. No. 5042551 shows that a one time use and throw away respirator uses the air pressure data to calculate the volume.

[0007] The respiratory flow or volume instrument is rather different in functions with those velocity devices due to the complexity of the respiration which includes the saturated vapor and ionic compound. The features of the instrument will change as time goes by while the flow types are used in a relatively simpler process.

[0008] Another thing is that the range of flow for the instrument is rather limited compared to the wide fluctuation of the human respiratory flows, from 0 to 14L/sec. This must be taken into consideration in the design. It is desirable that the intake piece is of sterilizable or abandonable type as it is used for breathing, which would be otherwise difficult for the present flow or pressure types.

[0009] To realize the miniature concept for these instruments and enhance the portability and lower the cost, the measurement element, in addition to other parts, must be low in power consumption and high in precision, a difficult requirement for the popular measurement elements. There is a great demand for the elements of miniature, low consumption of power and precision.

BRIEF OF THE INVENTION

[0010] Based on the above requirements, the invention is related to the application of the micro electromechanical technology to make the elements miniaturize and modularize with the aim at lessen the weight of the relative instrument and make portability possible. With lowered cost in production and material, it is easy for manufacture. In addition, this type of the instrument will be available for the combination with other sensors of similar use to widen its application.

[0011] Therefore, the product is termed the micro-machined hot-wire flow sensor for spirometer. The instrument has a crystal chip, a resistance with connectionpads; the chip area will be smaller than 2500×2500(micrometer)² in size, the resistance will be 1 to 1000 ohm, line width 5 to 1000-micrometer.

[0012] Also this invention includes the method of making such device at least:

[0013] (a) provide a chip base;

[0014] (b) surface preparation, which includes

[0015] (1) step to deposite a metal layer on top of the isolation;

[0016] (2) etching out the deposited metal layer which is outside the pattern;

[0017] (c) step to etch the chip base;

[0018] (d) step to make the connection pado for the resistance.

[0019] The flow sensor will have single or bi-directional capability of measurement according to the number of the resistance on the crystal chip base, together with the processor, respiratory pipe, liquid crystal LCD display and other devices, in particular for the portable or dest top type.

DETAILED EXPLANATION OF THE INVENTION

[0020] Unlike other air flow measurement devices, the respiratory functional measurement has a lot of limits and therefore some potential problems in operation. The elements must have sufficient mechanic strength and properly mounted without damage or deformation due to the high speed flow of air. The devices shall not block the respiratory airflow with overdue back pressure.

[0021] The measuring elements, in any type of instrument, must have stable output and sensitivity to ensure accurate measurement. Otherwise problems like compenoation may arise in connection with the temperature and composition of the airflow. The dust particles, drug and the salt in breath are likely to settle on the surface of the sensor causing pollution and drift of features and need compensation. The surface pollution, beside the above mentioned problems, will be risky in that infective diseases may spread. Therefore, the design of detection part will be preferably sterilizable or abandonable type. Water is one of the substances in the breath, which will decrease the sensitivity, because it condenses in the instrument and reduces the effective working area unless the instrument is warmed up to close to or above the body temperature. The working range of the respiratory measurement is quite wide from the static situation to the maximum of sportsman. To keep certain precision in a wide dynamic range, different piecewise linear or analysis modules may be required in design.

[0022] This invention takes the detail consideration for the production and the selection of materials to improve the characteristic of the instrument, which is quite different from the models mainly by improvement of the signal process. The instrument is featured in safe, economic and ease to use.

[0023] Thermal tachometer has the advantages of easy to use, light, portable, reliable, easy to clean and relatively cheap.

[0024] The invention takes reference to the making of semi-conductor. The thermal micro sensor is built on the chip base. The semiconductor, in addition to increasing the precision, can be used for the electronic circuit as well as sensing element. It is an intelligent instrument with less complexity on the external circuit and decreased noise interference.

[0025] Two types of modules and sensors are considered. One is abandonable type using low cost materials, which is quite simple in design and needs little protection. The type is intended for short time or simple measurement. Another type is of multifunctional with compound modules, which needs more protection and operates in relatively strict conditions with reliability and performance as the main consideration.

[0026] For the multifunctional type using thermal sensor, there comes some special requirements like the advantages of inertia, low power consumption, miniature, modularizable, arrayable, simple and productive. To prevent passivation and skewing, non-reactive to fluid material, noble metal, semi-conductor or even platinum will be used. If the sensor is designed for one time use or abandon type, common metal like nickel or chrome may be considered. As for the power consumption, the common sensors have power consumption of a couple or a dozen watts, working temperature of several hundred degrees to provide required sensitivity. The invention has done some improvements in the regard that it is not feasible to the portable models.

[0027] The following will be considered as to raise the resistance value, or to reduce the current through the sensor so as to lower the heat generation in a controlled manner.

[0028] The FIG. 1 shows the details of one direction respiratory measurement for the instrument. The resistor 1 will be in the repeating pattern in the circuit to be based on the glass 3; pads 2 a and 2 b are coupled with the ends of the resistor 1. Altogether resistor 1, pads 2 a and 2 b and chip base 3 have formed the single direction measurement instrument.

[0029] The FIG. 2 shows one side of the single direction respiratory measurement instrument. The glass coming 7740 is prepared for the base 4; the isolation layer 5 (silica) is produced by wet oxidation; to follow surface or base treatment will be carried out. The surface treatment by evaporation is to deposit the evaporated alloy of chromium (adhesion layer 6) and platinum (growing layer 7) on the glass base in the thickness of 500 angstrom for chromium and 2000-angstrom for platinum; or to put chrome layer 6 on the base 4 and then deposit platinum layer 7 on to layer 6. The wet etching process will proceed in order to remove the unwanted layer 6 and layer 7 (parts not required in design pattern) to finally form the resistive element as per the design diagram and wire layout. The following step will be decided whether the device is for one time use and the silica protective layer and the connective pad would be made (not shown in the Figure).

[0030] To reduce the heat capacity of the thermal wire, a bulk micromaching procedure must be made on it, by way of wet etching (diluted hydrofluoric acid) or dry etching (active ion) as base bulk treatment. The process does not require exposure or development as the resistant element (thermal wire) itself is resistive and will align automatically.

[0031] As shown in FIGS. 3 and 4, we can see the top and front view of the bi-directional respiratory flow measurement device. There are two major principles for the bi-directional respiratory measurement device: self heating and non self heating. In the Figures is shown the non self heating detection element without protection layer. Here we have chip 8, 2 non self heating resistance 9, 10, connection pads 9 a, 9 b and 10 a, 10 b, thermal wire 11 to be jointed to the chip 8. From FIG. 8 we have there is an isolation layer 12 on the base 8, 13 is a void as a result of base 8 fabrication (sketch of deposition layer omitted). Under the condition of non self heating balance and the air flow does not pass module 14, the temperature at both the ends of the self heating wire 11 and the non self heating resistance no.9 and no.10 (higher than body temperature) are the same; and when there is air flow pass from the left to the right to the sensor module 14 causing temperature changes at the non self heating resistance no.9 and no.10 (the temperature at the outcome on the right side of the resistance higher than the intake on the left). As a result, the difference of the resistance values can be adopted for calculating the parameters of the respiratory flow as has been done in the fixed voltage circuit.

[0032] The FIG. 5 is the front view of the bi-directional thermal respiratory measurement device with protection layer. The device is self heating module 22, having chip base 21, isolation layer 15, 2 self heating resistance 16 and 17, protection layer 20 and one shielding layer 19. The principle is similar to that of the non self heating type i.e. there is a difference between the two resistance due to the existence of the shielding 19. It is also possible to make a design for a temperature regulating circuit for the calculation of the air flow parameters.

[0033] In the selection of the materials for the device, the chips may be, in case of the low cost or one time use, glass, silicon or ceramic materials. For the growing layer between the chip base and the metal layer, chrome or titanium can be used. Copper or aluminum can be used for connection pads.

[0034] As for the processing proceduces like oxidation, wet or dry etching, chemical stacking, evaporation deposit and splashing deposit, there is no limit whatsoever but the differences by choosing different materials or resistances.

[0035] The only limit is that the device will be miniaturized in that the chip area be less than 2500×2500 micrometer, wire width between 5 to 100 micrometer, best 10 to 50 micrometer, resistance at 1 to 1000-ohm. The film obtained under the condition will be 0.1 to 0.5 micrometer, best at 0.1 to 0.3 micrometer, working current 1 to 100 milliampere, working temperature 40 to 200 degree, best at 40 to 50 degree.

[0036] As the requirement of conditions and sensitivity change, the wire width and resistance angle may be widened or revised, or to increase temperature compensation in the design, or to increase the unit density of the thermal wire for a better efficiency or higher resistance thus higher sensitivity.

[0037] The following is the sensor elements Hi-501 (Ni—Pt) found in the market, on which the comparison is made on the power consumption (example A): Resistance Sensor area Wire volume (ohm) (sq.f) (cu.f) Ther.capa. Hi-501 1.9 2.87 m × 10-7 3.93 × 10-12 148.8 Example A 1474 3.3 × 10-7 2.64 × 10-14 1

[0038] The invented device has small body and thus a low heat capacity and temperature decrease; with an increased sensing area the sensitivity is higher to offset the effect of decreased temperature.

[0039] Another sensor module (example B) has been compared with the market sensor Hi-501: Resistance Sensor area Wire volume (ohm) (sq.f) (cu.f) Ther.capa. Hi-501 1.9 2.87 m × 10-7 3.93 × 10-12 148.8 Example B 20 6.0 × 10-7 1.2 × 10-13 4.55

[0040] Example B is the revised version of the Example A, which has a higher resistance than Hi-501 and a reduced current and heat. The sensor area is large than Hi-501 and more sensitive to the flow speed thus offset the effect of decreased temperature.

[0041] The modularized components will make the device more powerful just as other models with additional sensors or modules to increase the functions of measurement and the value of the device. The respiratory measurement device made in the purpose will be used not only in the massive screening check but also in the field preventive procedures and family care having the very high practicable value.

BRIEF EXPLANATION OF DRAWINGS

[0042]FIG. 1 is the micrograph of the single direction micro machined hot wire flow sensor for spirometer.

[0043]FIG. 2 is the side view of the single direction micromachined hot wire flow sensor for spirometer.

[0044]FIG. 3 is the plan of the bi-directional micromachined hot wire flow sensor for spirometer.

[0045]FIG. 4 is the front view of FIG. 3.

[0046]FIG. 5 is the front view of the bi-directional micromachined hot wire flow sensor for spirometer.

ELEMENT REFERENCE

[0047]1. resistance

[0048]2. a connection pad

[0049]2.b. pad

[0050]3. chip base

[0051]4. base

[0052]5. isolation layer

[0053]6. deposited adheaoion layer

[0054]7. deposited metal layer

[0055]8. chip base

[0056]9. non self heating resistance

[0057]9 a. pad

[0058]9 b. pad

[0059]10. non self heating resistance

[0060]10 a. pad

[0061]10 b. pad

[0062]11. self heating wire

[0063]12. isolation layer

[0064]13. vacant

[0065]14. sensing module

[0066]15. isolation layer

[0067]16. self heating resistance

[0068]17. self heating resistance

[0069]18. vacant

[0070]19. screen

[0071]20. protection layer

[0072]21. chip base

[0073]22. self heating module 

1. A flow sensor, which includes at least one chip base and resistance grown on it and coupler, the chip is 2500×2500(micrometer)², resistance valued from 1 to 1000 ohm and wire width of 5 to 100 micrometer.
 2. The flow sensor of claim 1, wherein there is a deposited layer between the resistance and the chip base.
 3. The flow sensor of claim 1, wherein the resistance contains noble metal, polycrystalline silicon or conductive ceramic film.
 4. The flow sensor of claim 3, wherein the resistance contains noble metal.
 5. The flow sensor of claim 4, wherein the resistance contains platinum.
 6. The flow sensor of claim 1, wherein the resistance film is over 1000-angstrom.
 7. The flow sensor of claim 1, wherein the resistance is made in repeated way.
 8. The flow sensor of claim 1, wherein the chip base is of glass, silicon or ceramic materials.
 9. The flow sensor of claim 8, wherein the chip base is processed by etching to reduce heat capacity.
 10. The flow sensor of claim 9, wherein the etching is active ion etching or wet etching.
 11. The flow sensor of claim 10, wherein the etching is by buffered hydrofluoric acid.
 12. The flow sensor of claim 1, wherein the chip base has a single resistance to form a single direction sensor module.
 13. The flow sensor of claim 1, wherein the chip base has multi resistances to form bi-directional sensor module.
 14. The flow sensor of claim 1, wherein the resistance has a protection layer.
 15. The flow sensor of claim 14, wherein the protection layer is silica.
 16. The flow sensor of claim 15, wherein the connection pad material is common conductive metal.
 17. The flow sensor of claim 16, wherein the connection pad material includes copper, aluminum or other alloy.
 18. The flow sensor of claim 12 or 13, wherein the model is desktop or portable type.
 19. The flow sensor of claim 2, wherein the adhesion layer includes chromium or titanium.
 20. A method of making of the flow sensor, which contains at least: (a) Treatment of a chip base; (b) surface micromaching process, which will include at least: (1) procedure to grow a metal layer on top of the chip base; (2) etching out the attached metal layer which has grown outside the resistance pattern; (c) step to bulk micromaching the chip base; (d) step to make the connection pad for the resistance.
 21. The method of claim 20, wherein step (b) and (c) may change sequence.
 22. The method of claim 20, wherein the step (b)-(2) is wet etching.
 23. The method of claim 20, wherein a alloy of the attached layer and the growing layer may be prepared on the chip base or by sequential preparation.
 24. The method of claim 20, wherein the protection layer may be prepared before or after step (d).
 25. The method of claim 24, wherein the protection layer is prepared by chemical deposit or metal evaporation.
 26. The method of claim 20, wherein the chip base is glass, silicon or ceramic materials.
 27. The method of claim 20, wherein there is a step of making a isolation layer.
 28. The method of claim 27, wherein the isolation layer is silica.
 29. The method of claim 23, wherein the growing layer is made by chemical deposit or evaporation onto the chip base.
 30. The method of claim 20, wherein the etching of chip base is wet etching or active ion etching.
 31. The method of claim 30, wherein the wet etching agent is buffered hydrofluoric acid
 32. The method of claim 20, wherein step (b)-(2) is taken to etch out the attached or growing metal layer outside the resistance pattern to form the resistive layer.
 33. The method of claim 32, wherein the resistance has a wire width not less than 5 micrometer.
 34. The method of claim 33, wherein the resistance is 1 to 1000-ohm.
 35. The method of claim 20, wherein the growing layer contains noble metal, polycrystalline silicon or conductive ceramic film.
 36. The method of claim 25, wherein the growing layer contains noble metal.
 37. The method of claim 36, wherein the growing metal contains platinum.
 38. The method of claim 29, wherein the growing or evaporated or deposited film is 50 to 600 angstrom.
 39. The method of claim 29, wherein the growing or evaporated or deposited film is 1000-angstrom.
 40. The method of claim 20, wherein the resistance pattern is repeated form on the chip base.
 41. The method of claim 40, wherein the resistance pattern for single or multi design is based on the single direction or bi-directional flow measurement requirement.
 42. The method of claim 24, wherein the protection layer contains silica.
 43. The method of claim 20, wherein the connection pads material may be common conductive metal.
 44. The method of claim 43, wherein the connection pads material contains copper, aluminum or the alloy.
 45. The method of claim 43, wherein the making of the connection pads is etching and splashing or etching and evaporation.
 46. The method of claim 20, wherein the adhesion layer contains chromium or titanium.
 47. A method of making of the hot-wire flow sensor, whichl includes at least: (a) Treatment of a chip base; (b) surface micromaching process, which will include at least: (1) step to grow or to attach a metal layer on top of the chip base, which shall be evaprated or deposited film of 50 to 600-angstrom for attached film and 1000-gngstrom for the growing film evaporated or deposited; (2) etching out the attached metal layer which has grown outside the resistance pattern; (c) step to bulk micromach the chip base; (e) step to make the connection pad for the resistance; wherein resistance is 1 to 1000-ohm.
 48. The method of claim 47, wherein the sequence of (b) and (c) may change over.
 49. The method of claim 47, wherein the step (b)-(2) is wet etching.
 50. The method of claim 47, wherein a alloy of the attached layer and the growing layer may be prepared on the chip base or by sequential preparation.
 51. The method of claim 47, wherein the protection layer may be prepared before or after step (d).
 52. The method of claim 51, wherein the protection layer is prepared by chemical deposit or metal evaporation.
 53. The method of claim 47, wherein the chip base is glass, silicon or ceramic material.
 54. The method of claim 47, wherein there is a step of making a isolation layer after (a).
 55. The method of claim 54, wherein the isolation layer is silica.
 56. The method of claim 47, wherein the etching method of the chip base is wet etching or active ion etching.
 57. The method of claim 56, wherein the wet etching is using buffered hydrofluoric acid
 58. The method of claim 47, wherein step (b)-(2) is taken to etch out the attached or growing metal layer outside the resistance pattern to form the resistive layer.
 59. The method of claim 58, wherein the resistance has a wire width not less than 5 micrometer.
 60. The method of claim 47, wherein the growing layer contains noble metal, polycrystalline silicon or conductive ceramic film.
 61. The method of claim 60, wherein the growing metal contains noble metal.
 62. The method of claim 61, wherein the growing metal contains platinum.
 63. The method of claim 47, wherein the resistance pattern is repeated form on the chip base.
 64. The method of claim 63, wherein the resistance pattern for single or multi design is based on the single direction or bi-directional flow measurement requirement.
 65. The method of claim 51, wherein the protection layer contains silica.
 66. The method of claim 47, wherein the connection pad material may be common conductive metal.
 67. The method of claim 66, wherein the connection pad material contains copper, aluminum or the alloy.
 68. The method of claim 67, wherein the making of the connection pad is etching and splashing or etching and evaporation.
 69. The making of claim 47, wherein the growing layer contains chromium or titanium. 